neurotransmitters Flashcards
what is a classical neurotransmitter?
synaptic transmission from pre- to postsynaptic neuron
what is an auto neurotransmitter?
neurotransmitters act on pre-synaptic neuron (themselves)
acts on the same cell (or nearby cells) that released it
what is a retrograde neurotransmitter?
synaptic transmission from post to pre-synaptic cell (e.g cannabinoid)
how does a neurotransmitter act?
- direct effect on membrane potential – EXCITATORY and
INHIBITORY - indirect effect on membrane potential – positively or negatively MODULATORY
- indirect effect on transmitter release – generally negatively
MODULATORY
direct effect on membrane requires…
ion channels as they need to change the membrane potention
change in potentials in dendrites lead to…
EPSP (excitatory postsynaptic potential) or IPSP (inhibitory postsynaptic potential)
are EPSPs all or nothing?
no, they depend on ion influx amount
receptors activated by neurotransmitters rather than voltage
ligand gated ion channels on centre of synapse
metabotropic receptors (postsynaptic)
on outside of synapse
work via second messenger model (protein G)
modulate effectiveness of ligand gated ion channel e.g switch off when too much stimulation or positively modulatory of they are not activated efficiently
pre-synaptic autoreceptors and neurotransmitters
acting on own receptors
almost always negatively modulatory (auto neurotransmitters inhibit the further release of neurotransmitters from the presynaptic neuron)
why are almost all pre-synaptic auto-neurotransmitters negatively modulatory?
break in transmission (go, stop, go, stop) to separate each incoming signal
negative feedback via autoreceptors on the presynaptic neuron serves as a built-in mechanism to limit the amount of neurotransmitter released
what two types of neurotransmitters are constantly acting at the same time?
classical and auto
what are the classes of neurotransmitter?
- amino acids
- acetylcholine
- monoamines
- adenosine and ATP
amino acid structure
amine group, carboxyl group, variable R group and hydrogen
neurotransmitters co-opted from roles in protein structure and function
what are the most common amino acid neurotransmitters?
L-glutamate
glycine
γ-aminobutyric acid (GABA) (has amino and carboxyl group but not technically AA)
what is the smallest amino acid?
glycine
what is GABA made from?
glutamate
L-glutamate class
major EXCITATORY neurotransmitter in the CNS
acts at post-synaptic receptors (binds to glutamate receptors on the postsynaptic neuron leading to depolarisation)
some evidence for pre-synaptic receptors
GABA class
major INHIBITORY neurotransmitter
acts at pre- and post-synaptic receptors
released from a presynaptic neuron into the synapse, it binds to GABA receptors on the postsynaptic neuron, typically causing hyperpolarization
glycine class
INHIBITORY neurotransmitter in spinal cord and brain stem (main)
EXCITATORY co-agonist at glutamatergic
NMDA receptors (bind and allow calcium ions)
typically leads to the opening of chloride (Cl-) channels, allowing chloride ions to flow into the postsynaptic neuron, causing hyperpolarisation
other more unusual amino-acids can also
bind to the glycine site (ligand gated ion channel) e.g. D-serine
what receptors do inhibitory neurotransmitters act on?
anion channels (negatively charged ions across membrane)
what receptors do excitatory neurotransmitters act on?
cation channels (positively charged ions across membrane)
how does the stretch reflex work in terms of EPSP and IPSP systems?
synapse between EPSP and IPSP makes sure EPSP fires first to allow stretch and relax of muscle after
what is the effect of gabazine on GABA?
no effect (continued EPSP and IPSP)
